Study Guide for Dna Replication for Microbiology

Compare & Contrast Chromosomes

Prokaryotes Eukaryotes (humans)
Circular Linear
Single 2 Sets of Chromosomes
Reproduce Binary Fission 2 Alleles of each gene
(replicate itself) one allele or version each gene Cell nucleus
Cytoplasm (Site of transcription/Translation) Splicing
Small 30s and large 50s subunit 40s & 60s Subunit region of genes that code for proteins are called exons non coding called introns
Cells are made up of molecules, which are made up of atoms (smallest units of matter).
When atoms are joined together by hydrogen bonds they are molecules. (Hold DNA together)

DNA Replication

Said to be semiconservative
In bacteria DNA replication proceeds simultaneously in both directions, away from the origin of replication. DNA is the template or genetic material of the cell, the info for building proteins and RNA is located in the DNA.
The sequence of DNA that contains the info for a single protein or RNA is called a GENE.

• Purpose – to replicate dna in preparation for cell divison and to provide info for protein synthesis • Enzymes Involved in order – o Single Strand o Helicases – disrupt hydrogen bonds that hold two strands together. o Primase (RNA polymerase) – Provides a starting place for DNA polymerase III, synthesizes short strands of RNA (primers) that are complimentary to DNA o DNA Polymerase III - synthesizes the new strands of dna complimentary to the original. Must have a template to start, start adding nucleotides to the 3’ end o DNA Polymerase I – cleans RNA out of the new DNA, removes RNA primers and replaces them w/DNA o DNA Ligase – seals the breaks in the backbone of the new DNA, catalyzes the formation of covalent bonds along the sugar phosphate backbone between the fragments.
The neucleotides (simpler nitrogeneous base chemically bound w/sugar and phosphate group) joined together by bonds called ester bond. These 4 molecules are known as bases which determine nature of genetic code. Used are Adenine (A) Guanine (G) (purines) Cytosine (C) Thymine (T) (Pyrimidines)
Base Pairing is = Guanine molecule binds w/Cytosine use 3 Hydrogen bonds, Adenine bonds with Thymine use 2 hydrogen bonds. ACGU
For and RNA base use Uracil (U) not thymine and pairs with Adenine (A)
DNA Replication occurs in cytoplasm.

The lagging strand is the new strand of DNA that has its 3’ end pointing away from the replication fork. Because of this dna polymerase III synthesizes this strand in a bunch of small pcs called Okazaki fragments. By doing this DNA polymerase can stay w/the enzyme team as it moves around the circle.

The leading strand is built in one continuous piece the 3’ end points towards the replication fork.

Transcription

DNA makes RNA first step in protein synthesis. Transcription transfers information from language of nucleic acids to language of amino acids.
During process of transcription the info in the DNA is copied into a molecule of RNA.
The enzyme that reads the DNA and synthesizes the complementary molecule of RNA is RNA polymerase. RNA Polymearse locates the beginning of the gene it is going to copy by finding the promoter. (like a tab and beginning of file system)
Promoter indicates start of a gene (promoter sequence)

Template used is Messenger RNA (mRNA) transcribed from DNA and serves as a template for protein synthesis.

Nucleotides used are UC&G

Happens in the cytoplasm

Some RNA molecules like rRNA and tRNA directly perform a function for the cell.

If mRNA it will go to the ribosome to be translated into protein.

In Eukaryotes each gene has its own promoter and transcription terminator so each mRNA molecule is monocistronic containing info for just one polypeptide.
In Prokaryotes several genes may be organized together under one promoter forming an operon in which several genes are controlled together. molecule would be polycistronic containing info for several polypeptides.

Making proteins from the DNA code involves 2 processes: transcription and translation.

Translation

Translation of mRNA into protein involves the mRNA, the ribosome, which contains rRNA, and another type of RNA called transfer RNA tRNA. Each plays a role in translation.

FOR READING AN MRNA MOLECULE
The mRNA carries the blueprint for the protein from DNA

Ribosome is like the factory in which translation occurs. It organizes the process and has binding sites for the mRNA and tRNA.

The rRNA w/in the ribosome catalyzes bond formation between the amino acids building blocks of the protein.

The tRNA acts as a decoder, reading the mRNA code and bringing the correct amino acids into position in the growing polypeptide chain (polypeptide chain is a chain of amino acids that folds up to form a protein).
The anticodons in tRNA hydrogen bond to the codons in mRNA during translation. Like all nucleic acids this pairing occurs when the 2 strands are antiparallel to each other.
The specific pairing of anticodon to condon determines the sequence of amino acids in the polypeptide chain.

The mRNA code is read in codons, groups of 3 nucleotides. Each codon represents one amino acid.
There are 4 nucleotides in RNA C, G, A and U

The codon AUG is called the Start Codon (starting point of translation for mRNA) and this amino acid is called methionine

3 Codons UAA, UGA, UAG are called Stop Codons mark end point of translation and arrival of the enzyme release factor.
(These do not represent amino acids)

When reading mRNA you read from 5’ to 3’.